we are tyco integrated security. and we are sharper. >>> happening now, we're following breaking news. an alleged al qaeda-supported plot targeting a passenger plane thwarted. details on the arrests that have just been answer announced. >>> also, boston bombing suspect tamerlan tsarnaev's reported outburst at a cambridge, massachusetts, mosque. what set him off. >>> and was it a sign that he was turning radical? and is there a connection between one of the alleged bombers and militants in his native russia? cnn is on the ground there. we're looking for answers. i'm wolf blitzer. this is a special edition of "the situation room." >> announcer: this is cnn breaking news. >> and the breaking news coming in from canada right now where authorities have just announced the arrest as of two men believed to be part of an al qaeda-supported plot to attack a passenger train, a train potentially heading to the united states. they say the suspects were receiving support from al qaeda elements in iran. we want to stress, though, t